Redox-Bohr effect in electron/proton energy transduction: cytochrome c 3 coupled to hydrogenase works as a 'proton thruster' in Desulfovibrio vulgaris

 A central step in the metabolism of Desulfovibrio spp. is the oxidation of molecular hydrogen catalyzed by a periplasmic hydrogenase. However, this enzymatic activity is quite low at physiological pH. The hypothesis that, in the presence of the tetrahaem cytochrome c ₃, hydrogenase can maintain full activity at physiological pH through the concerted capture of the resulting electrons and protons by the cytochrome was tested for the case of Desulfovibrio vulgaris (Hildenborough). The crucial step involves an electron-to-proton energy transduction, and is achieved through a network of cooperativities between redox and ionizable centers within the cytochrome (redox-Bohr effect). This mechanism, which requires a relocation of the proposed proton channel in the hydrogenase structure, is similar to that proposed for the transmembrane proton pumps, and is the first example which shows evidence of functional energy transduction in the absence of a membrane confinement. Received: 2 April 1997 / Accepted: 23 May 1997     

现代生物技术在环境微生物学中的应用:I.基因探针和探针探测

现代生物技术在环境微生物学中的应用将发表系列综述文章。第一篇讨论基因探针和探针探测。这篇文章包含菌落转移或菌落杂交 ,Southern杂交和Northern杂交以及生物芯片。     

Environmental exposure to cadmium and factors affecting trace-element metabolism and metal toxicity

In the general population, food constitutes the major environmental source of cadmium (Cd) in nonsmokers. It is established that leafy vegetables, roots, and grains (wheat or rice) can accumulate relatively high amounts of Cd from the soil. Beef liver and kidney and shellfish are also major dietary sources of Cd. The daily intake of Cd in various parts of the world is different and depends on both the dietary habits and concentration of Cd in foodstuffs. Because of the long biological half-life of Cd in humans and absence of any specific indicators of its toxicity, the environmental exposure of Cd should be monitored in various countries. Although environmental Cd poisoning is rare, there are isolated reports on excessive exposure to Cd in Japan and Shipham, a zinc-mining town in England. The body retention and toxicity of Cd depends on various factors, such as daily intake, the form of Cd in food, its interactions with essential elements, and nutritional status of the population. Since kidney is considered a critical organ in Cd toxicity, the indicators of renal dysfunction have been widely used for evaluation of Cd poisoning in occupationally exposed people. It is unclear whether similar indicators can be used for monitoring environmental Cd exposure.     

Environmental influences on signal transduction through membranes: a retrospective mini-review

This mini-review is addressed to the question how the membranous environment may affect traffic of receptors and signalling from membrane-anchored receptors on the outside of cells to transducers and targets on the inside. Signal transduction by membrane-anchored receptors to the interior of the cell and eventually to the genome is a central issue in cellular regulation. In this context the role of membrane fluidity and of the cytoskeleton in restricting the mobility of proteins are discussed and the evidence for a structural order in membranes which could limit the mobility of proteins is scrutinised.     

Lateral transfer of eukaryotic ribosomal RNA genes: an emerging concern for molecular ecology of microbial eukaryotes

Ribosomal RNA (rRNA) genes are widely utilized in depicting organismal diversity and distribution in a wide range of environments. Although a few cases of lateral transfer of rRNA genes between closely related prokaryotes have been reported, it remains to be reported from eukaryotes. Here, we report the first case of lateral transfer of eukaryotic rRNA genes. Two distinct sequences of the 18S rRNA gene were detected from a clonal culture of the stramenopile, Ciliophrys infusionum. One was clearly derived from Ciliophrys, but the other gene originated from a perkinsid alveolate. Genome-walking analyses revealed that this alveolate-type rRNA gene is immediately adjacent to two protein-coding genes (ubc12 and usp39), and the origin of both genes was shown to be a stramenopile (that is, Ciliophrys) in our phylogenetic analyses. These findings indicate that the alveolate-type rRNA gene is encoded on the Ciliophrys genome and that eukaryotic rRNA genes can be transferred laterally.     

The environment,microbes and bioremediation: microbial activities modulated by the environment

Microorganisms in nature are largely responsible for the biodegradation and removal of toxic and non-toxic chemicals. Many organisms are also known to have specific ecological niches for proliferation and colonization. The nature of the environment dictates to a large extent the biodegradability of synthetic compounds by modulating the evolutionary processes in microorganisms for new degradative genes. Similarly, environmental factors often determine the extent of microbial gene expression by activating or repressing specific gene or sets of genes through a sensory signal transduction process. Understanding how the environment modulates microbial activity is critical for successful bioremediative applications.     

The cellular response to vascular endothelial growth factors requires co-ordinated signal transduction,trafficking and proteolysis

VEGFs (vascular endothelial growth factors) are a family of conserved disulfide-linked soluble secretory glycoproteins found in higher eukaryotes. VEGFs mediate a wide range of responses in different tissues including metabolic homoeostasis, cell proliferation, migration and tubulogenesis. Such responses are initiated by VEGF binding to soluble and membrane-bound VEGFRs (VEGF receptor tyrosine kinases) and co-receptors. VEGF and receptor splice isoform diversity further enhances complexity of membrane protein assembly and function in signal transduction pathways that control multiple cellular responses. Different signal transduction pathways are simultaneously activated by VEGFR–VEGF complexes with membrane trafficking along the endosome–lysosome network further modulating signal output from multiple enzymatic events associated with such pathways. Balancing VEGFR–VEGF signal transduction with trafficking and proteolysis is essential in controlling the intensity and duration of different intracellular signalling events. Dysfunction in VEGF-regulated signal transduction is important in chronic disease states including cancer, atherosclerosis and blindness. This family of growth factors and receptors is an important model system for understanding human disease pathology and developing new therapeutics for treating such ailments.     

Two-component signal transduction systems and regulation of virulence factors in <Emphasis Type=Italic>Xanthomonas</Emphasis>: a perspective

Two-component signal transduction systems (TCSTSs), consisting of a histidine kinase and a response regulator, play a critical role in regulating virulence gene expression in Gram-negative phytopathogenic bacteria Xanthomonas spp.. To date, 12 TCSTS genes have been identified, accounting for approximately 10% of the TCSTS genes in each genome that have been experimentally identified to be related to pathogenesis. These TCSTSs modulate the expression of a number of virulence factors through diverse molecular mechanisms such as interacting with DNA, protein-binding and involvement in second messenger metabolism, which generates a high level of regulatory versatility. Here we summarize the current knowledge in this field and discuss the emerging themes and remaining questions that are important in deciphering the signaling network of TCSTSs in Xanthomonas.     

Environmental sensing by chromatin: an epigenetic contribution to evolutionary change

Chromatin structure and function are regulated by families of protein-modifying enzymes that are sensitive to a variety of metabolic and environmental agents. These enzymes, and proteins that read the modifications they maintain, constitute a system by which environmental agents, such as chemical toxins and dietary components, can directly regulate patterns of gene expression. This review describes this environmental sensing system from an evolutionary perspective. It is proposed that persistent environmentally-induced changes in gene expression patterns can cause changes in phenotype that are acted upon by natural selection, and that epigenetic processes can potentially play central roles in evolution.     

Perfluorooctanoic Acid (PFOA): Environmental Sources,Chemistry, Toxicology,and Potential Risks

Attention regarding perfluoroalkyl and polyfluoroalkyl substances (PFAS) has increased in recent years, due to recognition of widespread environmental presence, recognition of a chemical structure that confers resistance to degradation, and reported health concerns. Historical common exposure sources include food, drinking water, occupational circumstances, and products in commerce (e.g., carpeting, clothing, paper products). Early-2000’s data showed perfluorooctanoic acid (PFOA) was present in blood samples from nearly all the U.S. general population (>99%). Alterations in industrial manufacturing processes, increased regulatory scrutiny, and advanced water treatment options have reduced the reported human body burden of PFAS in the U.S., including for PFOA. Human serum concentrations of PFOA, which do not identify the source(s) of exposure, have exhibited a substantial decrease (~63%) between the 1999–2000 and the 2013–2014 NHANES monitoring by the Centers for Disease Control and Prevention (CDC). With respect to both noncancer and potential cancer effects that may be associated with reported serum levels of PFOA, conclusions regarding an absence of effects, or insufficient information to suggest adverse effects, prevent a consistent conclusion about the occurrence and magnitude of human health effects. In the last several years, a number of state and federal agencies have developed health advisories or guideline values for drinking water exposure that are in the sub-ppb range. In 2016, a USEPA Health Advisory of 0.07 ppb was released, which stands in contrast to 2016 Health-based Values from Health Canada ranging from 0.2 ppb (PFOA) to 30 ppb, and a few other U.S. states with values even less than that of USEPA (e.g., MN, NJ, VT). Further work is necessary to distinguish in transparent fashion between drinking water levels that intentionally are set on a conservative basis to protect human health vs exposure levels that may be associated with tangible adverse effects.     

Redox-Bohr effect in the tetrahaem cytochrome c3 from Desulfovibrio vulgaris: a model for energy transduction mechanisms

 Using potentiometric titrations, two protons were found to participate in the redox-Bohr effect observed for cytochrome c ₃ from Desulfovibrio vulgaris (Hildenborough). Within the framework of the thermodynamic model previously presented, this finding supports the occurrence of a concerted proton-assisted 2e^– step, ideally suited for the coupling role of cytochrome c ₃ to hydrogenase. Furthermore, at physiological pH, it is shown that when sulfate-reducing bacteria use H₂ as energy source, cytochrome c ₃ can be used as a charge separation device, achieving energy transduction by energising protons which can be left in the acidic periplasmic side and transferring deenergised electrons to sulfate respiration. This mechanism for energy transduction, using a full thermodynamic data set, is compared to that put forward to explain the proton-pumping function of cytochrome c oxidase.     

Multifaceted effects of oligodendroglial exosomes on neurons: impact on neuronal firing rate,signal transduction and gene regulation

Exosomes are small membranous vesicles of endocytic origin that are released by almost every cell type. They exert versatile functions in intercellular communication important for many physiological and pathological processes. Recently, exosomes attracted interest with regard to their role in cell–cell communication in the nervous system. We have shown that exosomes released from oligodendrocytes upon stimulation with the neurotransmitter glutamate are internalized by neurons and enhance the neuronal stress tolerance. Here, we demonstrate that oligodendroglial exosomes also promote neuronal survival during oxygen–glucose deprivation, a model of cerebral ischaemia. We show the transfer from oligodendrocytes to neurons of superoxide dismutase and catalase, enzymes which are known to help cells to resist oxidative stress. Additionally, we identify various effects of oligodendroglial exosomes on neuronal physiology. Electrophysiological analysis using in vitro multi-electrode arrays revealed an increased firing rate of neurons exposed to oligodendroglial exosomes. Moreover, gene expression analysis and phosphorylation arrays uncovered differentially expressed genes and altered signal transduction pathways in neurons after exosome treatment. Our study thus provides new insight into the broad spectrum of action of oligodendroglial exosomes and their effects on neuronal physiology. The exchange of extracellular vesicles between neural cells may exhibit remarkable potential to impact brain performance.     

LPS介导细胞激活的信号转导：从CD14到p38MAPK通路的研究

近年来对脂多糖（ＬＰＳ）介导细胞激活的信号转导过程已取得实质性进展,ＬＰＳ与血浆ＬＰＳ结合蛋白（ＬＢＰ）结合被运输到单核巨噬细胞表面,与ｍＣＤ１４受体结合起起细胞激活。ＭＡＰＫ参与了ＬＰＳ激活细胞产生肿瘤坏死因子（ＴＮＦ）等活性物质的细胞内信号转导过程。ｐ３８ＭＡＰＫ对ＴＮＦ－α等细胞因子具有重要的调节作用。对ＬＰＳ激活细胞的信号转导研究呆能为治疗内毒素休克提供新的理论和思路。